Device for feeding an extrusion head for plastic material

ABSTRACT

A device for feeding an extrusion head for plastic material includes a main extruder connected to a main die for extruding a continuous main flow of material, and an auxiliary feed mechanism associated with the main die and selectively controlled to cover the outer exit flow of the main die with a surface layer. The auxiliary feed mechanism continuously conducts two auxiliary flows, a first flow forming the surface layer and the second flow being mixed with the main flow. An invertor valve permits selective exchanging of the two auxiliary flows such that the second flow can cover the main flow and the first flow can be mixed with the main flow.

BACKGROUND AND SUMMARY OF THE INVENTION

The subject of the present invention is a device for feeding anextrusion head for plastic material.

Devices of this kind, already known, are used especially for fabricatingby extrusion elongated products of plastic material presenting a coloredsurface layer.

It is usual to use two method for that:

1. Master-batches of colors are added to the mass of plastic material,

2. An additional extruder is used, which deposits a colored surface skinaround the extruded shape.

The second method has the advantage of saving on the coloring agentssince only a thin layer of the extruded product is colored.

The object of the present invention is to improve the feed devicesalready known, in order to apply the second method described above byachieving an instantaneous change of color without waste of material.

To this end, the device according to the invention is characterized inthat is comprises a main extruder connected to a main die and a feedmeans associated with the main die and capable of being selectivelycontrolled so as to cover the exit flow of the main die with a surfacelayer formed of successive segments, the appearance of which differs.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the subject of the invention will be described below,by way of example, referring to the appended drawing, in which:

FIG. 1 is a schematic top plan view showing an extrusion installationequipped with the device according to the invention,

FIG. 2 is a sectional view on a horizontal plane showing on a largerscale the extrusion head and its different feed orifices,

FIG. 3 is a sectional view along the line III--III of FIG. 2, and

FIG. 4 is a perspective view, partially cut away, of a length of asection of plastic material fabricated by the device of FIGS. 1 to 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The installation depicted in FIG. 1 is intended for the continuousproduction of a section of plastic material, for example, a bar, or atube, the cross-section of which may have any shape. It comprises a mainextruder 1 provided with a feed hopper 2 and driven by a motor 3 havinga reduction gear 4. Mounted at the end of the cylinder of this extruder1 is an extrusion head 5, the details of which are visible in FIG. 2. Onthe other hand, this extrusion head 5 is connected to an auxiliarytwinscrew .[.extruded.]. .Iadd.extruder .Iaddend.6 provided at itsrearward end with two feed hoppers 7 and 8. As is seen in FIG. 2, theauxiliary extruder 6 comprises two parallel cylindrical bores 9 and 10,in each of which a screw 11 or 12 rotates. These screws are driven by asingle speed-reduction gear 13 from a single motor 14, ensuring that thetwo screws constantly rotate at the same speed. As the dimensions of thescrews are the same, the flows of plastic material formed in the twocylinders 9 and 10 are of the same rate and reach the exit orifices 15and 16 of the extruder 6 in the same state of fluidity and compression.

FIG. 2 further shows the structure of the extrusion head 5. Mounted inthe cylindrical die body 17 are a main die 18, supported by a die holder19 and, in front of the die body 17, an auxiliary die 20 supported by adie holder 21 and fixed by a nut 22, the die holder being itself securedto the body 17 by a nut 23. The die 18 is fed at the rear of theextrusion head through the die holder 19 in a conventional manner. Thus,a direct connection of the die holder to the outlet of the cylinder ofthe extruder 1 is provided for.

The auxiliary extruder 6 is connected to the extrusion head 5 by ductswhich form two paths, these pass through a multiple-way valve 24, thebody 25 of which is fixed to the end of the body of the extruder 6 insuch a way as to be able to feed the head 5 laterally. The multiple-wayvalve 24 comprises a cylindrical valve needle 26. At one end, this valveneedle is provided with a prolongation of square cross-section (FIG. 3)permitting it to be rotated about its axis through an angle of 120° inorder to effect the conversion of the colors, as will be seen below. Oneof the two inlets 27 and 28 made in the body 25 ends facing a radialbore 29 passing through the valve needle 26 up to its axis, and theother facing a groove 30 which extends over 120° along the circumferenceof the valve needle 26. In the position depicted in FIG. 2, the groove30 causes the inlet 28 to communicate with an outlet 31 which ends,through the die body 17, in the outside surface of the die holder 21 andthence, via a distribution duct 44, feeds the conical space comprisedbetween the dies 20 and 18. By this route, the plastic material forcedback by the screw 12 forms a tubular film on the surface of theelongated product which is shaped in the die 18 with the materialsupplied by the main extruder. While the valve 24 is in the position ofFIG. 2, the material forced back by the screw 11 passes through theorifice 15 and into the duct 27. It arrives, as is seen in FIG. 3,through an axial duct 32 of the valve needle 26, in an outlet duct 33which is connected to a helical channel 34 made in the body 17 in such away as to encircle the die 18 and, via the groove 37, the receptacle 35,and a radial duct 36, to arrive in the inlet orifice 42 of the main die18. This material is therefore mixed with the material supplied by themain extruder, and as a result of its being projected in the form of ajet into the receptacle 35 from the groove 37, a rather rapid mixture ofthese two materials takes place.

It will be realized that the functions of the two auxiliary extruderscrews 11 and 12 may be reversed by rotating the valve needle 26 aboutits axis clockwise, as viewed in FIG. 2 through an angle of 120°. Inthis case, the inlet duct 27 is then connected directly to the outletduct 31, while the inlet duct 28 is connected via the radial bore 29 andthe axial channel 32 to the duct 33, to the helical channel 34, and tothe groove 37.

The use of the device described and the advantage of this device followsfrom FIG. 4, which depicts in cut-away perspective a length of section,for example, a cylindrical rod of plastic material, fabricated with thedevice described. It will be understood that each of the hoppers 7 and 8of the auxiliary extruder 6 is provided with a volumetric meteringapparatus 45, 46, permitting a certain quantity of coloring agent to beinserted in this hopper, with the plastic material which feeds it, thetwo colorant distributors containing materials of different colors, forexample, red and blue. It is therefore seen that if the valve needle 26is in the position of FIG. 2, and if the cylinder 10 is fed by a plasticmaterial provided with a batch of red colorant, the front portion.[.3a.]. .Iadd.38a .Iaddend.of the cylindrical section produced by theinstallation will be provided with a red surface film 39. However, theinstallation will permit changing the coloring of the surface film 39 inthe following segment 38b by a simple manipulation of the valve 24. Itwill be necessary beforehand to start up the colorant-metering apparatus45 of the cylinder 9 in order that the hitherto virgin plastic materialwhich is led into the receptacle 35 via the ducts 29, 32, and 33 startsto be colored blue, as depicted at 40 in FIG. 4. At the moment when thedesired red length of the elongated section has been produced, it willsuffice to switch over the valve 24. Immediately, the blue materialsupplied in the inlet duct 27 will be directed toward the auxiliary die20 and will give the surface film 39 a blue coloring, which will appearon the section, forming the segment 39b. The mass of red plasticmaterial which the screw 12 forces into the duct 28 will then be led viathe by-pass 34 into the receptacle 35 and will form a colored zone 41 inthe thickness of the section. After the reversal of the colors, theintroduction of the coloring agent into the hopper 8 by the meteringapparatus 46 can be stopped, so that the cylinder 10 will then carryvirgin plastic material, similar to that which enters the die 18 throughthe orifice 42 from the main extruder 1.

The system described lends itself to the production of any section ofplastic material produced continuously. It applies, for example, to theproduction of tubes, but equally to the production of insulating layerscovering an electric conductor, to the production of sheaths on cables,etc. The device permits, for example, producing a certain length X km ofelongated section covered with a surface layer of one color during agiven time, changing the visible color instantly, and producing a lengthY km of the same product covered with a surface layer of another color.The extruder continuously works virgin material. One of the twocylinders of the auxiliary extruder continuously works on the virginmaterial, the other on the colored material. The passing from one colorto the other is achieved by starting up the metering apparatuscontaining the coloring agent having the required color, then, at therequired moment, by manipulating the valve 24.

The starting up of the volumetric metering apparatus can be achievedautomatically by electronic means, such as a preset counter. Of course,the colors may be alternated, or sections successively having lengths ofseveral different colors may be produced.

What is claimed is:
 1. A device for forming a continuous elongatedelement of plastic material through extrusion, comprising:a mainextruder for a continuous main flow of a first plastic material;auxiliary feed means comprising two auxiliary flow exit orifices forcontinuously conducting auxiliary flows of a second and third plasticmaterial, respectively, all of said first, second and third plasticmaterials forming said main and auxiliary flows having differentconstitutions; a composite extrusion head having a die system, twoauxiliary flow inlet orifices, a main flow inlet orifice, a mixingreceptacle adjacent said main flow inlet orifice, an outlet orificedefined by an outlet die of said die system, and ducts within saidcomposite extrusion head connecting each of said auxiliary flow inletorifices to said outlet orifice through different routes, one of saidroutes connecting one of said auxiliary flow inlet orifices to saidmixing receptacle through a helical channel in an outer peripheralportion of said composite extrusion head, the other one of said routesconnecting the other one of said auxiliary flow inlet orifices with saidoutlet orifice through said die system to provide in said elongatedelement a continuous zone having in said element a predeterminedlocation; and inverter means connected to said exit orifices of saidauxiliary feed means and said auxiliary flow inlet orifices of saidcomposite extrusion head for exchanging the connections between saidauxiliary flows exit and inlet orifices.
 2. The device according toclaim 1 .[.in which.]. .Iadd.wherein .Iaddend.one of the auxiliary flowinlet orifices of the composite extrusion head is connected to ductsforming an outer layer on the elongated element, and the otherauxiliary-flow inlet orifice of the extrusion head is connected to meansfor mixing the auxiliary flow led through said other auxiliary flowinlet orifice with the main flow.
 3. The device according to claim 2,.[.characterized in that.]. .Iadd.wherein .Iaddend.the extrusion headcomprises a mixing cavity connected to a main inlet of the extrusionhead connected in turn to the main extruder and to the otherauxiliary-flow inlet orifice.
 4. The device according to claim 1,.[.characterized in that.]. .Iadd.wherein .Iaddend.the auxiliary feedmeans comprise an auxiliary extruder having two screws housed in twocylinders contained in a single body.
 5. The device according to claim4, .[.characterized in that.]. .Iadd.wherein .Iaddend.the two screws ofthe auxiliary extruder are driven by a single motor through theintermediary of a single speed-reduction gear.
 6. The device accordingto claim 4, .[.characterized in that.]. .Iadd.wherein .Iaddend.the twocylinders of the auxiliary extruder are each connected to a hopper forintroducing plastic material, and in that each of .[.these.]. .Iadd.said.Iaddend.hoppers is provided with a colorant-metering apparatus.
 7. Thedevice according to claim 1, .[.characterized in that.]. .Iadd.wherein.Iaddend.the inverter means comprises a valve having two inlet ways andtwo outlet ways, and a valve needle rotatable between two activepositions.
 8. The device according to claim 7, .[.characterized inthat.]. .Iadd.wherein .Iaddend.the valve needle is of cylindrical shapeand has an axial passage connected to a radial inlet way and a radialoutlet way, and an arcuate circumferential passage situated in a planeperpendicular to the axis of the valve needle, at the level of theradial inlet way, the radial inlet way and the ends of thecircumferential passage defining three segments of a circle of 120° eachon the circumference of the valve needle.
 9. A device for continuousextrusion of an elongated element of plastic material comprising acomposite extrusion head, a main extruder producing a main flow,auxiliary feed means including two exit orifices conducting twoauxiliary flows, and control means permitting the extrusion head to befed selectively so that one or the other of the said auxiliary flowsforms a particular zone in the elongated element, the compositeextrusion head further comprising two auxiliary-flow inlet orifices anda main-flow inlet orifice, respectively connected to the exit orificesand to the main extruder, and the control means comprising an invertercapable of exchanging the connections between the exit orifices of theauxiliary feed means and the said auxiliary-flow inlet orifices;whereinone of the auxiliary-flow inlet orifices of the extrusion head isconnected to ducts forming an outer layer on the elongated element, theother auxiliary-flow inlet orifice of the extrusion head is connected tomeans for mixing the auxiliary flow led through this orifice with themain flow; the extrusion head comprises a mixing cavity connected, onthe one hand, to a main inlet of the extrusion head connected in turn tothe main extruder and, on the other hand, to the said otherauxiliary-flow inlet orifice; and the inverter comprises a valve havingtwo inlet ways and two outlet ways, and a cylindrical shape valve needlerotatable between two active positions, the valve needle having an axialpassage connected to a radial inlet way and a radial outlet way, and anarcuate circumferential passage situated in a plane perpendicular to theaxis of the valve needle, at the level of the said radial inlet way, theradial inlet way and the ends of the circumferential passage definingthree segments of a circle of 120° each on the circumference of thevalve needle.
 10. The device according to claim 9, .[.characterized inthat.]. .Iadd.wherein .Iaddend.the auxiliary feed means comprise anauxiliary extruder having two screws housed in two cylinders containedin a single body.
 11. The device according to claim 10, .[.characterizedin that.]. .Iadd.wherein .Iaddend.the two screws of the auxiliaryextruder are driven by a single motor through the intermediary of asingle .[.speedreduction grear.]. .Iadd.speed reduction gear.Iaddend..12. The device according to claim 10, .[.characterized in that.]..Iadd.wherein .Iaddend.the two cylinders of the auxiliary extruder areeach connected to a hopper for introducing plastic material, and in thateach of .[.these.]. .Iadd.said .Iaddend.hoppers is provided with a.[.colorantmetering.]. .Iadd.colorant metering .Iaddend.apparatus..Iadd.
 13. A device for forming a continuous elongated element ofplastic material through extrusion, comprising:a main extruder for acontinuous main flow of a first plastic material; auxiliary feed meanscomprising two auxiliary flow exit orifices for continuously conductingauxiliary flows of a second and third plastic material, respectively,all of said first, second and third plastic materials forming said mainand auxiliary flows having different constitutions; a compositeextrusion head having a die system, two auxiliary flow inlet orifices, amain flow inlet orifice, an outlet orifice defined by said die system,and ducts within said composite extrusion head connecting each of saidauxiliary flow inlet orifices to said outlet orifice through differentroutes, one of said routes connecting one of said auxiliary flow inletorifices to a channel in said composite extrusion head communicatingwith said main flow inlet orifice, the other one of said routesconnecting the other one of said auxiliary flow inlet orifices with saidoutlet orifice through said die system to provide said elongated elementwith a continuous zone having a predetermined location; and invertermeans connected to said exit orifices of said auxiliary feed means andsaid auxiliary flow inlet orifices of said composite extrusion head forexchanging the connections between said auxiliary flows exit and inletorifices. .Iaddend. .Iadd.14. The device according to claim 13, in whichone of the auxiliary flow inlet orifices of the composite extrusion headconnects to ducts forming an outer layer on the elongated element, andthe other auxiliary flow inlet orifice of the extrusion head connectsthe auxiliary flow led through said other auxiliary flow inlet orificewith the main flow. .Iaddend. .Iadd.15. The device according to claim13, wherein the inverter means comprises a valve having two inlet waysand two outlet ways, and is rotatable between two active positions..Iaddend. .Iadd.16. The device according to claim 15, wherein the valveincludes a valve needle of cylindrical shape and has an axial passageconnected to a radial inlet way and a radial outlet way, and an arcuatecircumferential passage situated in a plane perpendicular to the axis ofthe valve needle, at the level of the radial inlet way, the radial inletway and the ends of the circumferential passage defining three segmentsof a circle of 120° each on the circumference of the valve needle..Iaddend. .Iadd.17. A device for continuous extrusion of an elongatedelement of plastic material, comprising a composite extrusion head, amain extruder producing a main flow, auxiliary feed means including twoexit orifices conducting two auxiliary flows, and control meanspermitting the extrusion head to be fed selectively so that one or theother of said auxiliary flows forms a particular zone in the elongatedelement, the composite extrusion head further comprising two auxiliaryflow inlet orifices and a main flow inlet orifice, respectivelyconnected to the exit orifices and the main extruder, and the controlmeans comprising an inverter capable of exchanging the connectionsbetween the exit orifices of the auxiliary feed means and said auxiliaryflow inlet orifices; whereinone of the auxiliary flow inlet orifices ofthe extrusion head is connected to ducts forming an outer layer on theelongated element, and the other auxiliary flow inlet orifice of theextrusion head connects the auxiliary flow led through the otherauxiliary flow inlet orifice with the main flow; and the invertercomprises a valve having two inlet ways and two outlet ways, and isrotatable between two active positions, said first active positiondirecting a first flow of the auxiliary flows to the outer layer of theelongated element and a second flow of the auxiliary flows to the zonewithin the elongated element, and said second active position directingthe first flow to the zone within the elongated element and the secondflow to the outer layer. .Iaddend. .Iadd.18. A device for extruding acontinuous elongated element of plastic materials having a coreencompassed by at least one outer sheath, comprising:a main extruder forextruding a continuous main flow of a plastic material; first auxiliaryfeed means for feeding a first continuous auxiliary flow of a firstmaterial, the first auxiliary feed means having a first exit orifice forcontinuously conducting said first auxiliary flow; second auxiliary feedmeans for feeding a second continuous auxiliary flow of a secondmaterial, the second auxiliary feed means having a second exit orificefor continuously conducting said second auxiliary flow; extruder meansfor extruding the elongated element comprised of said main flow and saidfirst and second auxiliary flows, the extruder means having a first flowpath for directing one material of said first and second materials tojoin with the main flow to form the core of the elongated element and asecond flow path for directing the other material of said first andsecond materials to form the outer sheath of the elongated element toencompass the core; and inverter means connected to the first and secondexit orifices of the first and second auxiliary feed means and the firstand second flow paths of the extruder means, for selectively exchangingconnections between the first and second exit orifices and the first andsecond flow paths. .Iaddend. .Iadd.19. A device for extruding acontinuous elongated element of plastic materials having a coreencompassed by at least one outer sheath, comprising: a main extruderfor extruding a continuous main flow of a plastic material; firstauxiliary feed means for feeding a first continuous auxiliary flow of afirst material, the first auxiliary feed means having a first exitorifice for continuously conducting said first auxiliary flow; secondauxiliary feed means for feeding a second continuous auxiliary flow of asecond material, the second auxiliary feed means having a second exitorifice for continuously conducting said second auxiliary flow; extrudermeans for extruding the elongated element comprised of said main flowand said first and second auxiliary flows, the extruder means having afirst flow path for directing one material of said first and secondmaterials to join with the main flow to form the core of the elongatedelement and a second flow path for directing the outer material of saidfirst and second materials to form the outer sheath of the elongatedelement to encompass the core; and inverter means connected to the firstand second exit orifices of the first and second auxiliary feed meansand the first and second flow paths of the extruder means, forselectively exchanging connections between the first and second exitorifices and the first and second flow paths and for selectivelyexchanging relative positions in the elongated element of the first andsecond materials. .Iaddend. .Iadd.20. A device for extruding acontinuous elongated element of plastic materials having a coreencompassed by at least one outer sheath, comprising:a main extruder forextruding a continuous main flow of a plastic material; first auxiliaryfeed means for feeding a first continuous auxiliary flow of a firstmaterial, the first auxiliary feed means having a first exit orifice forcontinuously conducting said first auxiliary flow; second auxiliary feedmeans for feeding a second continuous flow of a second material, thesecond auxiliary feed means having a second exit orifice forcontinuously conducting said second auxiliary flow; extruder means forextruding the elongated element comprised of said main flow and saidfirst and second auxiliary flows, the extruder means having a first flowpath for directing one material of said first and second materials tojoin with the main flow to form the core of the elongated element and asecond flow path for directing the outer material of said first andsecond materials to form the outer sheath of the elongated element toencompass the core; inverter means connected to the first and secondexit orifices of the first and second auxiliary feed means and the firstand second flow paths of the extruder means, for selectively exchangingconnections between the first and second exit orifices and the first andsecond flow paths and for selectively exchanging relative positions inthe elongated element of the first and second materials withoutinterruption of the first and second continuous flows. .Iaddend..Iadd.21. A device for extruding a continuous elongated element ofplastic materials having a core encompassed by at least one outersheath, comprising:a main extruder for extruding a continuous main flowof a plastic material; first auxiliary feed means for feeding a firstcontinuous auxiliary flow of a first material, the first auxiliary feedmeans having a first exit orifice for continuously conducting said firstauxiliary flow; second auxiliary feed means for feeding a secondcontinuous auxiliary flow of a second material, the second auxiliaryfeed means having a second exit orifice for continuously conducting saidsecond auxiliary flow; extruder means for extruding the elongatedelement comprised of said main flow and said first and second auxiliaryflows, the extruder means having a first flow path for directing onematerial of said first and second materials to join with the main flowto form the core of the elongated element and a second flow path fordirecting the other material of said first and second materials to formthe outer sheath of the elongated element to encompass the core; andinverter means connected to the first and second exit orifices of thefirst and second auxiliary feed means and the first and second flowpaths of the extruder means, for selectively exchanging connectionsbetween the first and second exit orifices and the first and second flowpaths, the inverter means being circular in cross-section and definingtwo conduits through the inverter means for connecting the first andsecond exit orifices and the first and second flow paths. .Iaddend..Iadd.22. A device for extruding a continuous elongated element ofplastic materials having a core encompassed by at least one outersheath, comprising: a main extruder for extruding a continuous main flowof a plastic material; first auxiliary feed means for feeding a firstcontinuous auxiliary flow of a first material, the first auxiliary feedmeans having a first exit orifice for continuously conducting said firstauxiliary flow; second auxiliary feed means for feeding a secondcontinuous auxiliary flow of a second material, the second auxiliaryfeed means having a second exit orifice for continuously conducting saidsecond auxiliary flow; extruder means for extruding the elongatedelement comprised of said main flow and said first and second auxiliaryflows, the extruder means having a first flow path for directing onematerial of said first and second materials to join with the main flowto form the core of the elongated element and a second flow path fordirecting the other material of said first and second materials to formthe outer sheath of the elongated element to encompass the core; andinverter means connected to the first and second exit orifices of thefirst and second auxiliary feed means and the first and second flowpaths of the extruder means, for selectively exchanging connectionsbetween the first and second exit orifices and the first and second flowpaths, the inverter means being movable between first and secondpositions, said first position connecting the first exit orifice to thefirst flow path for conveying the first material to the core of theelongated element and connecting the second exit orifice to the secondflow path for conveying the second material to the outer sheath of theelongated element, and said second position connecting the first exitorifice to the second flow path for conveying the first material to theouter sheath of the elongated element and connecting the second exitorifice to the first flow path for conveying the first material to thecore of the elongated element. .Iaddend. .Iadd.23. A device forextruding a continuous elongated element of plastic materials having acore encompassed by at least one outer sheath, comprising:a mainextruder for extruding a continuous main flow of a plastic material;first auxiliary feed means for feeding a first continuous auxiliary flowof a first material, the first auxiliary feed means having a first exitorifice for continuously conducting said first auxiliary flow; secondauxiliary feed means for feeding a second continuous auxiliary flow of asecond material, the second auxiliary feed means having a second exitorifice for continuously conducting said second auxiliary flow; extrudermeans for extruding the elongated element comprised of said main flowand said first and second auxiliary flows, the extruder means having afirst flow path for directing one material of said first and secondmaterials to join with the main flow to form the core of the elongatedelement and a second flow path for directing the other material of saidfirst and second materials to form the outer sheath of the elongatedelement to encompass the core; and inverter means connected to the firstand second exit orifices of the first and second auxiliary feed meansand the first and second flow paths of the extruder means, forselectively exchanging connections between the first and second exitorifices and the first and second flow paths, the inverter means beingcircular in cross-section and defining two conduits through the invertermeans, the conduits being movable between first and second positions,said first position connecting the first exit orifice to the first flowpath for conveying the first material to the core of the elongatedelement and connecting the second orifice to the second flow path forconveying the second material to the outer sheath of the elongatedelement, and said second position connecting the first exit orifice tothe second flow path for conveying the first material to the outersheath of the elongated element and connecting the second exit orificeto the first flow path for conveying the first material to the core ofthe elongated element. .Iaddend. .Iadd.24. A device for extruding acontinuous elongated element of plastic materials having a coreencompassed by at least one outer sheath, comprising: a main extruderfor extruding a continuous main flow of a plastic material; firstauxiliary feed means for feeding a first continuous auxiliary flow of afirst material, the first auxiliary feed means having a first exitorifice for continuously conducting said first auxiliary flow; secondauxiliary feed means for feeding a second continuous auxiliary flow of asecond exit orifice for continuously conducting said second auxiliaryflow; extruder means for extruding the elongated element comprised ofsaid main flow and said first and second auxiliary flows, the extrudermeans having a first flow path for directing one material of said firstand second materials to join with the main flow to form the core of theelongated element and a second flow path for directing the othermaterial of said first and second materials to form the outer sheath ofthe elongated element to encompass the core; and inverter meansconnected to the first and second exit orifices of the first and secondauxiliary feed means and the first and second flow paths of the extrudermeans, for selectively exchanging connections between the first andsecond exit orifices and the first and second flow paths to selectivelyexchange relative positions in the elongated element of the first andsecond materials, the inverter means being circular in cross-section anddefining two conduits through the inverter means, at least one conduitextending about a periphery of the circular cross-section to extendpartially circumferentially about the circular cross-section. .Iaddend..Iadd.25. A device for extruding a continuous elongated element ofplastic materials, comprising:a main extruder for extruding a continuousmain flow of a plastic material; first auxiliary feed means for feedinga first continuous auxiliary flow of a first material, the firstauxiliary feed means having a first exit orifice for continuouslyconducting said first auxiliary flow; second auxiliary feed means forfeeding a second continuous auxiliary flow of a second material, thesecond auxiliary feed means having a second exit orifice forcontinuously conducting said second auxiliary flow; extruder means forextruding the elongated element comprised of said main flow and saidfirst and second auxiliary flows, the extruder means having a first flowpath for burying one material of said first and second materials withinthe main flow and a second flow path for directing the other material ofsaid first and second materials to from an overcoat for the elongatedelement, the overcoat encompassing the main flow and the one material;and inverter means connected to the first and second exit orifices ofthe first and second feed means and the first and second flow paths ofthe extruder means, for selectively exchanging connections between thefirst and second exit orifices and the first and second flow paths sothat the material that was previously the overcoat can be buried withinthe elongated element and the material that was previously buried withinthe elongated element can be the overcoat. .Iaddend. .Iadd.26. A devicefor extruding a continuous elongated element of plastic materials,comprising:a main extruder for extruding a continuous main flow of aplastic material; first auxiliary feed means for feeding a firstcontinuous auxiliary flow of a first material, the first auxiliary feedmeans having a first exit orifice for continuously conducting said firstauxiliary flow; second auxiliary feed means for feeding a secondcontinuous auxiliary flow of a second material, the second auxiliaryfeed means having a second exit orifice for continuously conducting saidsecond auxiliary flow; extruder means for extruding the elongatedelement comprised of said main flow and said first and second auxiliaryflows, the extruder means having a first flow path for burying onematerial of said first and second materials within the main flow and asecond flow path for directing the other material of said first andsecond materials to form an overcoat for the elongated element, theovercoat encompassing the main flow and the one material; and invertermeans connected to the first and second exit orifices of the first andsecond feed means and the first and second flow paths of the extrudermeans, for selectively exchanging connections between the first andsecond exit orifices and the first and second flow paths, the invertermeans being circular in cross-section and defining two conduits throughthe inverter means, the conduits being movable between first and secondpositions, said first position connecting the first exit orifice to thefirst flow path for burying the first material within the elongatedelement and connecting the second exit orifice to the second flow pathfor conveying the second material to be the overcoat of the elongatedelement, and said second position connecting the first exit orifice tothe second flow path for conveying the first material to be the overcoatof the elongated element and connecting the second exit orifice to thefirst flow path for burying the second material in the elongatedelement, so that the material that was previously the overcoat can beburied within the elongated element and the material that was previouslyburied within the elongated element can be the overcoat..Iaddend.